Primary treatment mainly removes suspended solid pollutants from sewage, and most physical treatment methods can only meet the requirements of primary treatment.
The secondary treatment mainly removes colloid and dissolved organic pollutants (BOD, COD) in sewage, and the removal rate can reach over 90%, which makes the organic pollutants reach the discharge standard, and the removal rate of suspended solids reaches 95%, with good effluent effect.
The tertiary treatment can further treat the refractory organic matter, soluble inorganic matter such as nitrogen and phosphorus which can lead to eutrophication of water body. The main methods include biological nitrogen and phosphorus removal, coagulation and sedimentation, sand filtration, activated carbon adsorption, ion exchange and electrodialysis.
Extended data:
Requirements for sewage process selection: the existing primary treatment process should be reformed to improve the treatment effect. According to the actual situation, we should make full use of the existing treatment facilities and transform the structure or operation mode of septic tanks and contact tanks widely used in existing hospitals. If necessary, some facilities should be added to improve the treatment effect as much as possible, so as to meet the discharge standard of hospital sewage treatment.
Particles carrying viruses and germs are removed by coagulation and sedimentation (filtration), which improves the disinfection effect and reduces the dosage of disinfectant, thus avoiding the adverse impact of excessive dosage of disinfectant on the environment. Hospital sewage enters the regulating pool through septic tank, with automatic grille in front of the regulating pool and lifting pump in the regulating pool.
Baidu encyclopedia-sewage treatment